1. Field of the Invention
The present invention relates to a process for preparing a briquette from a coal for use in coke production.
2. Description of the Prior Art
Recently, because of the marked development of the iron and steel industry, the demand for coke, which is one the main raw materials for the industry, has been increasing more and greatly. However, a hard coking coal of high grade, which is indispensable for the production of metallurgical (iron manufacturing) cokes, has not only been rising in price due to the scarcity of resources in the world, but also has become difficult even to secure. Therefore, studies have been directed toward processes the manufacture a blast furnace coke of good quality wherein relatively low-grade coals are employed, i.e. non coking coal or poorly coking coal which heretofore have not been regarded as suitable for this purpose, or toward processes where a larger amount of soft cooking coal is blended. In the latter processes there have been proposed various kinds of caking substances and preparation processes using these low grade coals.
Processes for blending briquettes, which is one of techniques for preparing metallurgical cokes, have also been proposed in order to solve the subjects mentioned above. The, the conventional briquette preparation technique is a process wherein a bituminous substance having a softening point of about 60.degree.-80.degree. C is used as a caking substance, mixing is effected by using a low speed rotating type mixer in which its mixing tool operates at a peripheral velocity of lower than 5.0m/sec., such as a pug mill etc., while passing through steam of 120.degree.-250.degree. C, and the heated mixture is briquetted. It is important in this process to regulate the softening point of the caking substance, the temperature of the passing steam and the mixing time. Owing to various restriction the mixing time of about 4-7 minutes has been adopted on an industrial scale. In order to maintain the strength of the briquette from such a process, a caking substance must be properly selected so that it has a softening point corresponding to the temperature of steam and therefore a large amount of steam must be passed. However, if a caking substance having a softening point of above 120.degree. C is used, it may solidify occasionally before briquetting according to the heating conditions, even if steam of above 200.degree. C is passed. Consequently, there has been a strict limitation in the selection of caking substances, and only coal tar pitch having a softening point of 60.degree.-80.degree. C has been used. Moreover, there are many restrictions in installing and constructing a new steam generator for supplying steam due to the strengthening of pollution control regulations, and large expenses are incurred to comply with these regulations.